1. Field of the Invention
The present invention relates to a method of controlling the aspect ratio of a nano-structure, a method of producing a nano-structure using the same and a nano-structure produced thereby. More particularly, the present invention relates to a method of easily controlling the aspect ratio of a nano-structure, which can be effectively used in various fields including a positive active material for a rechargeable battery, an electrode material for a storage battery, a redox catalyst, a molecule support, and so on, and, and by which various nano-structures of desired sizes can be easily produced according to the necessity.
2. Description of the Related Art
As the market in fields of cellular phones, notebook computers, electric cars, and so on, is on the rise, energy storage technology is gradually gaining attention.
Accordingly, electrochemical devices have gained highest attention, and major part of the electrochemical devices includes rechargeable batteries and capacitors. In order to improve the capacity and commercial viability of the electrochemical devices, active research into new material and design is under way. Currently commercially developing batteries include Ni-MH, Ni—Cd, Pb—PbSO4, lithium ion batteries, and so on.
Specifically, lithium ion batteries are drawing attention owing to their various advantages, including a high operation voltage and high energy density, and the market of the lithium ion batteries is gradually expanding.
According to expansion of the lithium ion battery market, serious problems are encountered, including the sharp increase in prices of cobalt that is the most desirable positive electrode material and environmental pollution caused by cobalt. Under the circumstances, research into alternative materials is intensively conducted. In addition, particle sizes of metal oxide used as an electrode of a battery are reduced to a nanometer scale, a surface area of the metal oxide is increased, the charging/discharging speed and capacity of the battery can be increased, efforts to synthesize nano-scale electrode materials have continued. Attempts that have been made up to now were simply directed toward reduction in the particle size to a nano scale, but there was not any research into a nanowire having a very large aspect ratio. The same is true of another electrochemical device, that is, a high-capacity capacitor.
A vital part in the upcoming research is how to control the shape of a metal oxide using a cost-efficient process. An electrode has conventionally been fabricated by a solid-state reaction at a high temperature of greater than several hundreds of degrees, giving an electrode structure in a micrometer scale. Presently, there are numerous method of forming nano-sized metal oxide, which are widely accepted in the academic and industrial fields, including template synthesis, evaporation, laser ablation, sputtering, chemical vapor deposition, physical vapor deposition, and so on, which are, however, quite poor in commercial viability. Even if a technique is commercially viable, it may be applied only to high-priced products.
In addition, a drawback to the conventional manganese oxide nano-structure growth technology is in that the aspect ratio of a nano-structure cannot be controlled. In order to utilize the nano-structure freely in forming a nano-device, it is necessarily possible to synthesize a nano-structure having a length adjustable according to necessity. Thus, controlling the aspect ratio of the nano-structure is crucial to nano-device applications. It is well known that electrode characteristics or catalytic activity of a metal oxide nano-structure are closely related with crystal forms or specific surface area of the nano-structure associated with the aspect ratio of the nano-structure.
Therefore, physical properties of the metal oxide can be optimized by controlling the aspect ratio of the nano-structure. In addition, hybrids of various molecules and metal oxide are necessary for nano-bio applications in the fields of, for example, drug carriers or DNA storage units. To this end, it is necessary to optimize an interaction between a target bio-molecule and metal oxide by adjusting a size of the metal oxide to be adapted to a size of the target bio-molecule.